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As Ecosystems, Cities Yield Some Surprises

By Hillary Rosner August 11, 2011 1:47 pmAugust 11, 2011 1:47 pm

Researchers at Boston University have been measuring the ebb and flow of carbon dioxide emissions on different days of the week.

In Boston, scientists measuring the city’s greenhouse gas emissions have found what they call a “weekend effect,” a clear drop-off in the amount of carbon dioxide entering the city’s atmosphere on Saturdays and Sundays. In Fresno, researchers have discovered that backyard water use increases with wealth, as does backyard biodiversity. And in Los Angeles, ecologists studying the city’s “ecohydrology” have calculated that planting a million new trees, an idea with fairly universal appeal, would have the drawback of increasing water consumption by 5 percent.

The researchers, who presented their findings this week at the Ecological Society of America’s annual meeting in Austin, Tex., are all involved in a nascent program to understand the nation’s cities, home to 80 percent of the population, as functioning ecosystems. The goal is to educate urbanites about their environment and how they can act to make it more sustainable.

The program, called Ultra, for Urban Long-Term Research Area, is a joint effort of the National Science Foundation and the Forest Service. A total of 21 projects are under way, including two in New York City. In establishing financing (known as Ultra-Ex grants) for exploratory sites in 2009, the science foundation called urban sustainability one of “the greatest challenges to the long-term environmental quality of the nation.”

At a research site in Fresno, Calif., overseen by Madhusudan Katti, an ecologist at California State University’s campus there, the aim is to untangle the interactions between city water policy, outdoor water use at homes and biodiversity to help inform policy. On the average, wealthier households in Fresno use more water in their yards, yet not because the water is more affordable for them: the city has no metering system, so residents pay a fixed monthly rate.
Reducing water use is considered crucial to guaranteeing long-term sustainability, yet Dr. Katti found that using less water could cause local bird diversity to decline.

“Half the population globally lives in cities, but we don’t have a conceptual understanding of how cities work as dynamic systems,” Dr. Katti said. “We need to generate that understanding.”

Nathan Phillips, an ecologist at Boston University who runs one of the city’s two Ultra-Ex sites, told the audience at the conference that his project, which includes rooftop plant experiments both in and outside the city as well as measurements of greenhouse gases, had revealed a “pulsing type of urban metabolism.”

In a visible signature of human activity, emissions of carbon dioxide increase during the week and decline on the weekends, he said. The next step is putting sensors on 160 Boston buses and identifying the locations of natural gas leaks around the city.

In New York City, one Ultra-Ex project based at Columbia’s Lamont-Doherty Earth Observatory is exploring links between public health, green spaces, and ecosystem services, or nature’s ability to perform functions like cleaning the air and water or preventing flooding. The project is studying seven green roofs, including one at the main post office building on Eighth Avenue in Manhattan, to understand their role in preventing sewage from spilling into the city’s waterways during heavy rains.

Some Ultra-Ex projects have a social justice component. In Syracuse, the research helped prevent the installation of a sewage pipe in a low-income neighborhood. Scientists were able to show that installing features like green roofs and porous pavements could reduce storm water runoff.

Just as these research sites are beginning to reveal how such urban ecosystems function, federal budget cuts are calling their future into question. At the ecology meeting, a few dozen Ultra researchers met to discuss how to merge their independent projects into a more closely knit network with an online hub, with or without a central financing source. Cities, after all, will still live and breathe and eat and sweat regardless of what happens in Washington — where there is, by the way, an Ultra-Ex site researching the environmental factors that cause neighborhoods to decline or flourish.

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